Electric discharge apparatus



June 1, 1937. o. w. PIKE Er AL ELECTRIC DISCHARGE APPARAZUS Filed March 15, 1934 Fig.2.

Fig. I.

Inventors.

Otis W.Pike, Thomas A.Elder*, 9

Their ttovneg.

Patented June I, 1937 UNITED STATES PATENT OFFICE N. Y., assignors to General a corporation of New York Electric Company,

Application March 15, 1934, Serial No. 715,630

6 Claims.

The present invention relates to electric discharge devices, more particularly to full-Wave rectifiers for translating large currents.

An object of the present invention is to provide an improved device of the type mentioned which depends on conduction by gas ionization and in which arc-back between any of the electrodes during operation is substantially precluded. Another object is to provide a power rectifier in which a rugged electrode structure is employed, positioned rigidly within the envelope.

Other objects and features will be apparent as the specification is perused in connection with the accompanying drawing in which Fig. 1 is an elevational view in perspective of the rectifier improved in accordance with the present invention; Fig. 2 is an enlarged elevational view, partly in section, of the electrode structure shown in Fig 1; Fig. 3 is a sectional view taken along the line 3-3 in Figs. 1 and 2, as seen in the direction of the arrows, while Fig. 4 is a sectional view of one of the seals shown in Fig. 1. Figs. 5 and 6 are fragmentary views showing modifications in which the electric discharge device employs a metal envelope, and Fig. 'l is a fragmentary view in section of a modified form of seal employed in connection with metal envelopes.

In Fig. 1, numeral I designates a cylindrical envelope of vitreous material which is closed at the top by a hemispherical portion and terminates at the bottom in a reentrant glass plate or header member 2 carrying four upstanding glass cylinders 3. These cylinders support the electrode structure and provide for the necessary leadingin conductors as will be explained hereinafter.

The electrodes consist of an indirectly heated cathode 4, shown more clearly in Figs. 2 and 3, and a pair of oppositely disposed anodes 5 which may take the form of arcuate corrugated strips of metal. The cathode may consist of a metal chamber 4 from which extend a large number of transversely disposed metal disks 6 which are secured to the metal chamber in any suitable and well-known manner, as for example that shown and claimed in the Hull Patent No. 1,924,319 and the Pike Patent No. 1,924,375, assigned to the same assignee as the present invention. These disks are preferably coated on both sides with an electronically active material, such as barium oxide. Metal rods 1 (shown in Fig. 3) extend longitudinally through the disk structure so as accurately to space the disksfrom one another at their edges to render the cathode structure rigid and in addition to conduct. load and heating current to the cathode. The cathode chamber before, but also through the various contains a heater which may consist of an elongated spiral 8 of tungsten wire, the purpose of which is to heat the cathode surface to an electron-emitting temperature.

About the cathode structure, there are positioned several heat shields 9, l and II spaced in any suitable manner from one another, for example, by indentation, the purpose of which is to minimize heat radiation by the cathode and hence to increase its operating efliciency. As shown, the two inner shields 9 and [0 are of much shorter length than the outer shield II. All of the heat shields are preferably closed at the top by metal disks, two of which are illustrated and designated by reference character l2. The rods 'I extend not only through the disks 6, as pointed out hereinheat shields and are connected to the outermost shield II. The intermediate heat shield I 0 may be secured to the electrode structure by a pair of metal bands l6 which fit snugly about each end of the shield and are welded or otherwise secured to a large metal plate, web or partition member ll, the purpose of which will be described hereinafter. The outer heat shield H which extends for about the same length as the plate I 1, may be secured thereto in like manner, i. e. by welding. The heat shields 9, l0 and I l are provided with several large slot-like openings l8, of about the same length as the cathode, equally spaced about the peripheries of the shields and in register with one another.

As will be seen more clearly in Fig. 3, the plate or web IT extends entirely across the middle portion of the tube, dividing the cylindrical envelope into two equal longitudinal and physically separate sections. The web is maintained in its central position by means of upturned flanges l9 at the outer edges which serve to stiifen the memher. The width of the web preferably is less than the interior dimension of the envelope, when the latter is constituted of glass, in which case there is provided a metal wedge 32 of nickel wire at each upper edge of the web toprevent any lateral movement of the latter and at the same time to allow for expansion of. the web during iube exhaust or operation. As shown in Figs. 1 and 2, the web l'l extends for a considerabledistance beyond each end of the cathode and other parts of the electrode structure. The web may be laterally supported in a direction normal to its width by a pair of rigid rod members 20 which are secured to the web in any suitable manner and which terminatein bent portions fitting snugly against the envelope.

Between the heat shield II and the anodes 5, there is a metal shield 2|, formed of two semicylindrical portions and secured in any suitable manner, as by welding, to the metal plate |1 so as to be concentric with the shielded cathode structure. The shield member 2| is provided with a pair of elongate openings 22 of somewhat larger size than those in the heat shields, and positioned in line between the cathode and the respective anodes. These openings are out of register with the openings I8 in the heat shields and as illustratively exemplified, are positioned midway therebetween. As shown more clearly in Fig. 2, the metal shield 2| extends along the length of the tube for approximately the same distance as the length of the anodes.

The anodes may consist of heavy rugged material, corrugated metal, as shown, and may take an arcuate form so as to be concentric with the cathode and the surrounding heat shields. The anodes are preferably hung from a pair of upright U-shaped frame members 23 which are held away from the central plate member H, in spaced relation with one another, by means of metal straps 24 secured to rectangular blocks 25 of lava, alumina or other insulating material. These blocks may be secured by screws (not shown) to the web l1. The frame members 23 terminate at the lower end of the tube as shown, in inwardly bent portions 26 which are welded or otherwise secured to cap members 21 constituted of a metal which may be sealed, preferably without strain and even with a butt joint, to a glass cylinder 28, as shown more clearly in Fig. 4. An example of a suitable metal and glass for a seal of this kind is disclosed and claimed in the Burger and Hull application Serial No. 105,250, filed January 4, 1934, and entitled Glass-to-metal seals, assigned to the same assignee as the present invention. As pointed out in the Burger and Hull application, a metal which may be advantageously employed for this purpose, i. e. without the necessity of tapering or otherwise deforming the metal, may consist of approximately 18% cobalt (Co), 28% nickel (Ni) and 54% iron (Fe), and the glass may have the following approximate composition: 65% silica (S102), 23% boric oxide (B203), 1% sodium oxide (NazO) and 5% aluminum oxide (A1203). A glass of this composition may be readily fused to many of the common glasses of which the envelope and the upstanding cylinders 3 are made. A metal sleeve 29 which surrounds a flexible cable 30 and is swedged thereto, may be welded at its free end to the interior surface of the cap member 21. A supporting connection is provided by a rigid U-shaped member 38 directly between the central web I1 and one of the cap members 21. One of the ends of the heater is connected to another of the cap members 21, the other end of the heater being welded to the interior surface of the cathode compartment. It will be evident that the four cap members 21 together with their associated conductors 29 and flexible cables 30 bring separate connections out through the tube from each of the anodes, from the cathode structure which is electrically connected to the web I! and from the free end of the heater contained within the cathode. If desired, a capsule 3| containing material for absorbing deleterious gases during manufacture and operation of the tube may be secured to any one of the frame members 23.

After evacuation of the envelope in the most approved and well-known manner, and with the electrodes in place, inert gas such as argon or neon at a pressure of approximately 100 microns may be admitted to the envelope, or a globule of mercury (not shown) provided, which under operating conditions produces a vapor pressure of approximately 50 microns when the temperature of the mercury condensate is between 60 and 80 C.

A tube of the type described, operates on the gas ionization principle in which large currents are conducted between the cathode and each anode. For this purpose alternating current voltage is applied between the respective anodes and the cathode and when proper circuits are connected thereto, the tube will rectify both halfwaves of the alternating current voltage.

In case mercury or other vapor-producing substance is employed as a source of positive ions, the vapor pressure within the tube depends upon the temperature of the coolest part of the envelope, i. e. upon the temperature of the mercury condensate. Electrons emitted by the cathode collide with the mercury-vapor atoms and produce ionization. Atoms of argon or other inert gases may also produce ionization, as is well known. These positive ions are attracted toward the cathode and neutralize the normally negative space charge around the cathode and this action, in turn, results in a relatively low voltage drop between each anode and the oathode, with consequent low energy loss in the tube.

The current between the cathode and each anode takes on the character of an arc-like or glow discharge and follows a tortuous path from the cathode through the aligned openings IS in the heat shields, through the openings 22 in the outer shield member 2| which are out of line with those in the heat shields, finally reaching the anode 5. Inasmuch as for a given tube of practical dimensions, with 1000 volts on each anode, approximately 12%; amperes per anode or 25 amperes average current for the full-wave device may be rectified, it will be apparent that the electrical conditions within the device are severe. The electronically active material coated on the cathode disks tends to sputter off and be driven on to the anode or to condense on any cool surface within reach. This material of course moves out radially from the cathode through the openings I8 and would normally reach the anodes 5 if it were not for the fact that the openings 22 in the shield 2| are out of line with the openings |8 in the heat shields 9, H) and II and thus a solid metal wall or barrier is presented to the sputtered material. The cylinder 2| may therefore be termed a sputter shield since it serves to prevent active material from reaching the anodes 5. It will of course be understood that any active material deposited on the anodes 5, may give rise to arc-back between the anodes and the cathode, particularly when the tube is carrying large currents. Moreover, the solid wall orbarrier effect of the sputter shield 2| permits only a curved path for the current flow which has been found to be advantageous in that the anode is not subjected to direct bombardment by positive ions on the inverse voltage cycle and hence, does not become sufficiently heated to give off deleterious gases. Itis also apparent that this shield furnishes additional heat shielding for the cathode.

By extending the member I for a considerable distance along the web l1, even as far as the lower edge thereof, as shown, a support is provided for the lower. set of blocks 25 to which the channel members 23 are secured. It is Y the standpoint of undesired discharges, the web butt joints.

may extend the full length of the envelope. While we'have shown a central partition for dividing the envelope into'only two electrically separate sections, which utilize the same cathode but different anodes, we may provide a plurality of partitions or webs to constitute a multi-sectioned tube suitable for translating alternating current of any number of phases. a

It will be noted that in the structure provided for the leading-in conductors, no tapering of the metal where it is sealed to glass is necessary since as pointed out hereinbe fore, asubstantially strainless seal, i. e. one in which theglass and metal have approximately the same thermal expansion throughout the temperature range between 0 C. and the-softening temperature of the glass, is provided which .permits the use of Such a seal maybe madein any suitablemanner, but we prefer to wet the metal by the glass in a high frequency furnace such as is disclosed and claimed in the McArthur application Serial No. 705,251, filed January 4, 1934,-

and entitled Glass-tmmctal seals, assigned to the same assignee as the present application.

A tube of the type described is of very rugged construction and the electrodes are rigidly supported within the envelope without the necessityfor complicated structures including reentrant stems, clamping devices, etc. trode structure including the anodes. and all the metal work maybe fabricated as a unit, and the parts accurately assembled before the unit is placed within the envelope.

It will be noted that the Web H is preferably at cathode potential, consequently it is feasible to substitute metal for the glass of the envelope as shown in Fig. 5 in which case the entire 'envelope would also be at cathode orother fixed potential. Obviously in this case, there is no necessity for the rod members 20 because the member I! may be welded or otherwise secured' directly to the envelope. It will be understood that, if .desired, the web I 1 may be'suitably' insulated from the cathode structure, for example, by means of strips 33 of insulating material which -may be interposed between the flanges I 9 and the metal envelope 34, and a potential assigned to the envelope other than cathode potential. In the case of a metal envelope, slight changes should be made in the structure for bringing out the leading-in conductors sothat the various conductors may be insulated from one another.

and from the envelope. Obviously, no cathode leading-in conductor is necessary in the case of the metal envelopebecause the member Il may be secured, as by welding, to the interior periphery of the metal cylinder which is then necessarily at cathode potential. In the case of a evident that the lower portion of the plate member ll serves as a shield for the enclosed heater lead.

cathode, said heat shield having Moreover, the elecmetal envelope in which the web member is for providing-the necessary insulation for leading-in conductors through ametal envelope is shown and claimed in the Nolte application Serial No. 716,111, filed March 17, 1934 and entitled Leading-in conductor seals and assigned to the same vassignee as the present application. As disclosed in the Nolte application and illustrated in Fig. 7 of the present drawing, the upstanding glass member 3 may be advantageously replaced by a metal cylinder 35 and between the cap member 2! and the metal cylinder 34 referred to, there may be provided a glass cylinder- 36 of the proper composition sealed substantially strain-free atthe temperatures reached during the sealing process, to each of the metal terminating members. Other structures for providing the necessary insulation between the leading-in conductors and the metal container will readily suggest themselves to those skilled in the art.

What we claim as new and desire to secure by Letters Patent of the United States is:

I. An electric discharge device comprising an envelope containing a cathode coated with electronically active material, and a plurality of anodes mounted about the cathode, an ionizable medium in the envelope at a pressure under operating conditions, sufiicient'to support anarclike discharge, a heat shield mounted about the discharge openings, a sputter shield interposed between the heat shield and the anodes, said sputter shield having discharge openings out of line with the openings in the heat shield.

I 2. An electric discharge device comprising an envelope containing a cathode coated with electronically active material, and a plurality of anodes mounted about the cathode, an ionizable medium in the envelope at a pressure under operating conditions, suificient to support an'arc-like discharge, a heat shield mounted about the cathode, said heat shield having discharge openings, a sputter shield interposed between the heat shield and the anodes, said sputter shield having discharge openings out of line with the openings in the heat shield and electrically connected to the cathode.

3. An electric discharge device comprising an 4. An electric discharge device comprising an envelope of elongate configuration containing a cathode coated with electronically active material, and a pair of anodes mounted on opposite sides of the cathode, an ionizable medium in the envelope at a pressure under operating conditions, suiiicient to support an arc-like discharge, a heat shield mounted about the cathode, said heat shield having discharge openings, a sputter shield interposed between the heat shield and the anodes, said sputter shield having discharge openings out of line with the openings in the heat shield, and a partition extending longitudinally through the envelope and electrically separating the anodes from one another thereby preventing undesired discharge.

5. An electric discharge device comprising an envelope of elongate configuration containing a cathode coated with electronically active material, and a pair of anodes mounted on opposite sides of the cathode, an ionizable medium in the envelope at a pressure under operating conditions, suflicient to support an arc-like discharge, a heat shield mounted about the cathode, said heat shield having discharge openings, a sputter shield interposed between the heat shield and the anodes, said sputter shield having discharge openings out of line with the openings in the heat shield and a metal partition extending longitudinally through the envelope and electrically separating the anodes from one another thereby preventing undesired discharge, said partition being connected to the cathode.

6. An electric discharge device comprising an envelope containing a cathode and a plurality oi anodes mounted respectively on opposite sides of the cathode, an ionizable medium in the envelope at a pressure under operating conditions, suflicient to support an arc-like discharge, a shield mounted about the cathode, said shield having discharge openings in line with said cathode and the anodes, and a barrier between each of said anodes and the cathode, in line with said openings, for preventing current flow in a straight line between the respective anodes and the oathode through each of said openings.

OTIS W. PIKE. THOMAS A. ELDER. 

